<!DOCTYPE html>
<html>
<head>
  <style>
    #testElem {
        border: 1px solid black;
        background: yellow;
        contain: layout size;
        width: 300px;
    }
  </style>
  <script>
    function go() {
        /* trigger an incremental reflow.
         * Note: elem.style is undefined for MathML elements, so we have
         * to use setAttribute().
         */
        testElem.setAttribute("style", "width:150px");
    }
  </script>
</head>
<body onload="go()">
  <math>
    <mtable id="testElem">Change my size</mtable>
  </math>
</body>
</html>
